This is the least important reason to maintain species diversity, but... Olympia oysters are delicious. Very different flavor from the dominant Pacific species. I'm hopeful there's a win-win here where we're able to improve the ecosystem that also benefits from a financial incentive.
I'd die laughing to see a concerted conservation campaign around this:
> Stop killing all the delicious things! Think of how many fruits, how many oysters, how many fish you havn't tasted! Save them all so you can eat them all!